The invention relates to an imaging system for the fluorescence-optical visualization of a two-dimensional or three-dimensional object and to a method for the fluorescence-optical visualization of a two-dimensional or three-dimensional object.
Such an imaging system for the fluorescence-optical visualization of a two-dimensional or three-dimensional object, in particular of the body of a patient and the organs and/or tissue regions thereof, has an illumination unit and a capturing unit, which firstly illuminate the object, i.e. irradiate it with an optical radiation of visible and/or infrared light, and secondly capture an optical signal generated in or at the object on account of the irradiation. For this purpose, the illumination unit is designed for emitting optical radiation in a predetermined wavelength range in order to illuminate the object and excite a fluorescent substance contained in the object, while the capturing unit is designed and provided for capturing an optical signal from the region of the object and for splitting the optical signal into a fluorescence signal having a first wavelength range and a signal of visible light having a second wavelength range.
The fluorescence signal arises in a human body for example as a result of the excitation of a suitable contrast agent, for example in the form of a dye such as indocyanine green (ICG), which corresponds to a fluorescent dye that is already used conventionally in medicine as an indicator substance (e.g. for photometric liver function diagnosis and fluorescence angiography) in the case of heart, circulatory, liver and eye diseases. For this purpose ICG is administered for example intravenously or else for diffusion on the skin and is naturally eliminated from the body with a half-life of approximately 3-4 minutes depending on liver performance. ICG can be present as a sodium salt in powder form and can be dissolved in various solvents. The absorption and fluorescence spectrum of ICG is in the near infrared range. The maximum of the fluorescence spectrum is different depending on the solvent: it is at a wavelength of approximately 830 nm in blood, and at approximately 820 nm in water (given an excitation wavelength of e.g. 765 nm).
In the case of an imaging system known from US2006/0108509 A1 visible light together with an excitation radiation in the infrared range is radiated onto an object, and an optical signal is captured from the region of the object. By means of beam splitters in the form of a mirror arrangement, the optical signal is then split into a first signal, corresponding to a fluorescence signal, in the infrared range and a second signal in the range of visible light. The signals are subsequently converted into electronic data signals by a plurality of electronic converters, processed further in a processing unit and displayed on a monitor.
In the case of an imaging system known from U.S. Pat. No. 6,293,911 B1 in a similar manner, an object is excited and an optical signal is captured from the region of the object. The optical signal is split into a signal of visible light and a fluorescence signal by means of a mirror arrangement, the signal of visible light subsequently being decomposed into a red, a green and a blue component (the so-called RGB colors) using a dichroic prism and processed further, as is also known from color video cameras, for example.
Both the arrangement in US2006/0108509 A1 and the system in U.S. Pat. No. 6,293,911 B1 use separate mirrors in order to separate fluorescence signals from signals of visible light. The resultant arrangements require a certain structural space for the provision of the mirrors and the propagation of light between the mirrors. Moreover, an extension of the channels of the arrangement for example for splitting and processing further signals is not readily possible.